I. Field of the Invention
The present invention relates generally to devices and methods for removing bone, and more particularly to such devices and methods used in performing tibial osteotomies in humans.
II. Description of Prior Art
Many devices have been developed over the years to facilitate the removal of bone from the leg in order to correct certain malalignments of the legs. Malalignment of the anatomical axis and the mechanical axis along the tibia and femur in the coronal plane can lead to degenerative osteoarthritis of the knee. The abnormal loading stresses caused by such malalignment can be quite painful, and corrective surgery is often required to place the anatomical axes of the tibia and femur in proper alignment. The most common surgical procedure employed to correct tibiofemoral malalignment is the upper tibial osteotomy, which removes a wedge-shaped portion from the cancellous bone of the metaphysis of the tibia. The size of the wedge to be removed is determined by the surgeon upon an analysis of the gait of the patient, the degree of tibiofemoral malalignment, the patient's indication of the precise location of pain, and several other factors. After the wedge is removed, the head and distal portions of the tibia are slowly pulled toward one another to close the resultant gap. When the gap is closed, a bracket is used to keep the internal bone surfaces together until the surgical wound is properly healed. Because the tibia and femur are now in proper alignment, further degeneration of the knee joint is arrested and pain is reduced.
One such method and apparatus for performing tibial osteotomies is disclosed in U.S. Pat. Nos. 5,021,056 and 5,053,039, both issued to Hofmann, et al. The apparatus comprises, in part, a first guide assembly which grips the medial and lateral surfaces of the knee and serves to guide a saw blade in making the horizontal, or transverse, cut in the wedge. The first guide assembly is stabilized against the knee by at least two pins placed through the first guide assembly and into the head of the tibia. With the first guide assembly in place, a third hole in the first guide assembly is used to guide a drill bit completely through the head of the tibia adjacent to the location of the transverse cut. A depth gauge is then used to determine the width of the bone for the transverse cut. Below the stabilizing pins and the measurement hole, the first guide assembly includes a slot through which the saw blade must pass to make the transverse cut from the lateral side of the knee. Rather than cutting completely through the tibia head, however, the transverse cut is made such that an 8-10 millimeter bridge of cancellous bone is left on the medial side to act as a hinge during closure. The saw blade is then withdrawn from the transverse cut.
A second guide assembly is then placed at the site to provide guidance for the second, or oblique, cut. The second guide assembly includes a blade-shaped extension which is inserted into the transverse cut, and the guide is stabilized by the same two pins used for the first guide assembly. A plurality of oblique slots are formed into the second guide assembly which correspond to various angles for the oblique cut. The oblique slots are formed such that the end of the saw blade will meet with the end of the transverse cut previously made, thus enabling the cutting and removal of a wedge-shaped portion of bone from the tibia. After the wedge has been removed, the second guide assembly is removed from the osteotomy site.
To close the gap created by the removal of the wedge, an L-shaped plate is placed over the guide pins and across the portions of bone to be drawn together. The two guide pins are then removed and replaced by a pair of cancellous screws to hold the upper section of the plate against the bone surface. Next, a hole is drilled into the lateral tibia below the gap so that a ratcheted compression device can be employed to close the gap through plastic deformation of the medial bridge. One jaw of the compression device includes a rod which is inserted into the hole, while the other jaw includes a hook which engages the L-shaped plate. After the gap is closed, the compression device is removed, and additional cancellous screws are used to firmly attach the plate across the surgical wound.
While the Hofmann apparatus and method do appear to provide favorable results, there are several aspects to both the surgical procedure and the design of the components which allow the introduction of human error. For example, when the first guide assembly is placed across the knee, there is no way for the surgeon to obtain fluoroscopy images of the transverse cut. It may be possible for the first guide assembly to be constructed of a radiolucent material, but it would be more advantageous to dispense with this device in its entirety.
Second, after the transverse cut is made, the saw blade is removed from the cut so that the blade-shaped portion of the second guide assembly may be inserted. On occasion, the lower tibia must be slightly displaced, either to remove the saw blade or to fully insert the second guide assembly. This movement of the tibia will necessarily cause deformation of the medial bridge and can sometimes cause it to fracture. If the medial bridge is completely fractured, an additional plate may be required to keep the bones together, leading to significant healing complications and a possibility of loss of correction. Ideally, the tibial osteotomy should be performed with instruments that eliminate these concerns.
Third, once the wedge of bone has been removed, the guide pins are taken out of the tibia and replaced by cancellous screws to hold the L-shaped plate. While this procedure does not ordinarily cause problems, the screws may not accurately follow the hole left by the drill bit or the pins. In some instances, the screws may deviate away from the hole and push through the upper surface of the tibia head, because the operation is performed very close to the knee joint. Optimally, the screws which hold the plate to the tibia should use the drill bits or pins as a guide to verify that they will not harm other areas of the tibia.